Tubulars such as casing or liners are most frequently joined with threaded connections. These connections when used in a drilling environment are subject to fatigue from the dynamic loads encountered during such drilling procedures. There is a need to enhance the fatigue life of such connections.
Friction stir welding techniques have been used to join tubulars where the tubulars are butted together or alternatively with a shim introduced between them and the welding apparatus is rotated around the tubulars on its own axis while pushed into the junction of the tubulars as shown in US Publication 2010/0136369. In U.S. Pat. No. 3,779,446 the axis of the welding apparatus in FIGS. 3 and 4 is parallel to the tubulars being joined as the apparatus rotates on its axis and is brought to contact end flanges in the tubulars to be joined. Other similar references are U.S. Pat. Nos. 4,063,676; 5,071,053; 6,142,360; 3,848,793; 7,168,606.
The common theme to many of these techniques is to insert a ring shaped member in a notch formed by ends of adjacent tubulars and apply radial force to the ring while it is rotated. The present invention applies axial force to a rotated or oscillating coupling through the tubular ends that are to be joined to opposing ends of the coupling. An induction heating device can be deployed at each connection to preheat the connection location before the friction welding begins during or/and after the connection is made. The use of the present invention enhances energy efficiency, weld quality, material selection choices and connection reliability; while enabling reduced equipment size and cost. These and other features of the present invention will be more readily apparent from a review of the detailed description and the associated drawing while recognizing that the full scope of the invention is to be determined from the appended claims.